There are 2 spellings for armor. One without the u, “armor”, which is American, and one with the u, “armour”, which is British.
Not-with-standing the spelling, armor plates have been used for over 3000 years. It began with leather and evolved through various reinforced woods to steel and modern composites such as Kevlar and ceramics. The goal of all developments in Armoring is to provide greater protection using the “lightest” materials available.